Science News

A Publication of the Delta Stewardship Council

Sacramento Regional Wastewater Treatment Plant
(Outlined in yellow)

The Delta Stewardship Council voted to support a permit that would require more thorough treatment of Sacramento-area wastewater.

“If we’re serious about the Delta and its future, we have to start doing things differently - upstream, downstream, and in the Delta itself,” said Council Chair Phil Isenberg. “The science is clear, and so is the need for action.”

The National Pollutant Discharge Elimination System (NPDES) permit that regulates the discharge of treated wastewater from the Sacramento Regional Wastewater Treatment Plant to the Sacramento River is more than 10 years old, and Central Valley Regional Water Quality Control Board staff has recommended a new tentative permit that would bring the Sacramento plant up to the same level of treatment required of all other large wastewater dischargers to the Delta. Among other measures, it would reduce the plant’s daily discharge of total ammonia into the Sacramento River by 13 tons, from 14 to one. The Central Valley Regional Water Control Board is scheduled to take up the matter at its meeting December 9-10 in Rancho Cordova.

In recent correspondence to the Central Valley board, Isenberg shared findings by the Council’s Lead Scientist Cliff Dahm that the proposed permit is consistent with the best available science and if implemented, would improve water quality and the Delta ecosystem by limiting ammonia discharges into the Sacramento River.

In a memo to Isenberg, Dahm commended the regional water board on its comprehensive assessment of the issues associated with the Sacramento Regional Wastewater Treatment Plant and noted that there is growing recognition of multiple stressors affecting the Delta ecosystem. However, he said, it is also clear that the current balance of nutrients in the ecosystem - particularly total ammonia levels - ranks among the more important of these stressors. Excessive amounts of nutrients can promote the growth of harmful algae, which can degrade water quality both as a habitat for the Delta’s native aquatic species and as a source of drinking water. Discharge from the plant also affects the composition of the phytoplankton of the Delta waterways and affects the distribution and productivity of the aquatic plant community.

“The suggestion by the discharger that there is sufficient assimilative capacity in the Sacramento River to absorb 14 tons of total ammonia per day runs counter to the mounting chemical and biological evidence downstream of the discharge,” Dahm wrote. “It is time to make the (Sacramento plant) a key component of the overall Delta solution by bringing current treatment technology into the 21st century.”

The tentative permit under consideration requires total ammonia removal reduction utilizing a technology known as full nitrification followed by denitrification, which would necessitate the construction of new facilities and longer retention of wastewater on the plant site. In addition to the total ammonia reduction measures, the permit would require new microfiltration and UV disinfection.

“It is time to make the (Sacramento plant) a key component of the overall Delta solution by bringing current treatment technology into the 21st century.”

--Cliff Dahm, Delta Stewardship Council Lead Scientist

Sacramento wastewater officials estimate that full compliance with all terms of the permit would require about $2 billion in capital costs, which could be partially offset through local partnerships or by state or federal funding assistance. Regulators have proposed a 10-year period for compliance with the new permit.